Quantum information science holds immense promise for new and enhanced
technologies in communications, computation, and precision measurement, as well
as being closely linked to the fundamentals of quantum mechanics. One approach
to realising these goals is to encode information onto single photons, the individual
quanta of light. In this thesis, I .make use of a source of pairs of photons based on
spontaneous four-wave mixing in microstructured fibre, which generates correlated
signal and idler photons equally spaced in frequency above and below a bright
pump laser powering the process. This source is well suited to demonstrating
small-scale quantum information tasks involving a few quantum bits due to its
brightness ' (the pump power required to reach a high generation rate is lower
than comparable sources using bulk crystals) and its high coupling efficiency into
standard optical fibre and photon detectors. Also, the use of a microstructure
allows the dispersion properties of the fibre to be precisely engineered, adding
control over the photons' wavelengths and spectral properties.
Quantum interference is observed between signal photons in a Hong Ou Mandel
dip with a visibility of 73%, which is thought to be limited mainly by impurity
in the spectral state. Also, polarization entanglement between a signal-idler pair
is generated with a fidelity of 87%. The source is then used in an interferometric
setting to demonstrate enhanced sensitivity to optical phase changes and path-lengths
compared to what can be achieved with classical light, and interference
fringes are observed with down to a sixth of the wavelength of the classical pump
laser. Using two sources of entangled pairs and a 'fusion' gate, three and four
photon entangled GHZ states are produced with fidelities of 75% and 67% respectively.
A rotated version of the four photon state is used to demonstrate three
logic gates in the one-way model of quantum computing, the Hadamard H, the T
phase rotation, and the controlled-NOT. Finally, the entangled state is extended
to graph states with more complex structures, using path degrees of freedom to :
add extra qubits to photons. A graph-state error correcting code is demonstrated.